The invention relates to a method for a quantitative detection of a linear and rotary movement. The method uses an optical device that contains a light emission device, a grid device containing translucent areas and opaque areas, a detection device and an evaluation circuit coupled to the detection device.
Optical encoders are used to detect the rotation angle or, respectively, a length and a direction of a rotary movement or, respectively, linear movement of moving bodies. The essential components of such a device are the emitter system, a grid plate, normally a grid disk or a grid straight edge, and the detector system. The emitter system normally contains a light-emitting diode. The light beam emitted from the laser diode is modulated by the grid plate. The grid plate is connected to a moving body and has a periodic opening pattern. The detector system detects the transmitter signal (modulated by the grid plate) from the laser diode and, at the output, and supplies information relating to the light beam and the direction of movement.
Previous versions of optical encoders contain a light-emitting diode having additional optics, the grid plate and a detector array with evaluation logic. At the emitter end, a light beam is produced, which illuminates the detector array as uniformly as possible. The detector array contains at least two photodiodes, which are disposed in the direction of a linear movement, or tangentially with respect to a rotary movement. The distance between the photodiodes is one quarter of the grid disk period, and the signals from two adjacent photodiodes are phase-shifted through 90xc2x0 with respect to one another. The output signals from the photodiodes are suitably processed in an evaluation circuit in order to supply the position and direction of movement.
Two photodiodes disposed in a line are sufficient to define the position and direction. However, embodiments having four photodiodes disposed in a line are widely used in the prior art, for example as described in U.S. Pat. No. 4,654,525. This configuration and the evaluation circuit which is coupled to the photodiodes additionally allow compensation for light intensity fluctuations in the laser diode.
The previous systems are thus limited to a configuration of a plurality of photo receivers on the detector side. Such a limitation may be disadvantageous for several reasons. It is thus of primary importance for an optical encoder to be constructed in a space-saving manner. This requirement is thus difficult to satisfy from the start on the detector side.
It is accordingly an object of the invention to provide a method for a quantitative detection of a linear and rotary movement which overcomes the above-mentioned disadvantages of it the prior art devices of this general type, whose detector side can be manufactured more easily. In particular, an object of the present invention is to specify such a device that can be operated with only one photo receiver.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optical device for quantitative detection of linear or rotary movements. The optical device has a light emission device, a grid device containing translucent areas and opaque areas, and a detection device. An evaluation circuit is provided which is coupled to the detection device. The light emission device has at least two light emitters that are disposed alongside one another in the direction of a linear movement or tangentially with respect to a rotary movement. The light emitters can be actuated in a pulsed mode at the same or different clock frequencies, and in that their radiation strikes the detector alternately. The detection device has a photo receiver that is of such a size and is positioned such that the radiation from all the light emitters can be detected by it and the evaluation circuit is configured for separating the signals which originate from different light emitters. From the detected signals the position and the movement direction can be derived.
The photo receiver and the evaluation circuit are preferably integrated in a single semiconductor chip.
The clock frequency which is applied to the emitters is much higher than the modulation frequency of the grid plate, that is to say the frequency at which the light beams normally pass through the grid openings when the moving body is moving.
In a first embodiment of the invention, a control device is provided for the light emitters, which is configured in such a manner that it actuates the light emitters with control pulses at the same clock frequency, but with a defined phase shift which may be, for example, 90xc2x0.
In a second embodiment of the invention, a control device is provided for the light emitters, which is configured such that it actuates the light emitters with control impulses at a different clock frequency.
Vertical resonator light emission devices, in particular vertical cavity surface emitting lasers are advantageously used as the light emitters, since they are distinguished by particularly low divergence and a high light yield.
The optical encoder according to the invention has, in particular, the advantage that it can be operated with a single photo receiver.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for a quantitative detection of a linear and rotary movement, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.